The present invention relates generally to an enlarging lens barrel, and it relates more particularly to an improved enlarging lens barrel for use which, when mounted on an enlarger, characters or figures representing the aperture value of the lens iris diaphragm are illuminated by the light from a light source of the enlarger.
When a positive print is produced with the use of an enlarger, it would be highly advantageous, if the aperture value of the enlarging lens is visible in a dark room. In this connection, there is described in the German laid-open Patent Application No. 1924016 an enlarging lens barrel, comprising an inner sleeve having an opening in a given circumferential position and a guide passage adapted to guide the light from the enlarger light source into an opening; a single reflecting surface adapted to reflect the light traversing the guide passage in a radially outward direction, a transparent light guide having an outer peripheral surface on which are marked a series of characters representing aperture values; and a diaphragm setting ring adapted to rotate along the outer circumferential surface of the inner sleeve and having an observation window in a portion thereof in front of the opening.
With this enlarging lens barrel, the light from a light source of the enlarger traverses the guide passageway and is reflected by the single reflecting surface of the light guide, thereby illuminating a series of characters representing aperture values. When the aperture of the iris diaphragm is varied by rotating the diaphragm setting ring, then there can be observed through the observation window only the characters representing the aperture value corresponding to the aperture of the iris diaphragm which has been set at that time.
However, this enlarging lens barrel possesses numerous disadvantages, among which is the limitation imposed on the outer diameter of the coupling portion to the enlarger, since the inner diameter of the enlarging lens coupling portion is predetermined or fixed, and in that there is a limitation imposed on the outer diameter of the lens holder, because the diameter of the lens is predetermined or fixed, such that the aforesaid guide passageway may not be enlarged in width in a radial direction. Accordingly, the light which traverses this guide passageway and reflected by the aforesaid single reflecting surface in a radially outward direction in narrowed in width to pencil of light rays in the axial direction of the inner sleeve, resulting in the illumination of only a limited region of the aforesaid outer circumferential surface. This then results in the limitation of rendering the respective illuminated characters very small, with the resultant difficulty of reading such characters.
On the other hand, most of enlarging lens barrels commercially available are provided with only a click type or non-continuous type diaphragm setting ring, whereby the aperture of an iris diaphragm may be set in a stepped or increment manner in cooperation with the angular position of the ring. However, this type of enlarging lens barrel involves shortcomings in that when a subject image of a color negative is to be printed on a printing paper in an attempt to obtain a positive print having a good color balance, the aperture of the aforesaid iris diaphragm should be more finely adjusted than that of a unit setting graduation. This type of enlarging lens barrel is not suitable for this purpose for such reason.
To this end, there has been proposed a so-called enlarging lens barrel of the manually preset type, which is provided with a click-type or non-continuous type diaphragm setting ring and with a non-click type or continuous type diaphragm setting ring, whereby when the click-type diaphragm setting ring is set to an aperture value such as 5.6, the non-click type or continuous type diaphragm setting ring may be rotated continuously within a range from the maximum aperture value to 5.6. However, the aforesaid two setting rings of this enlarging lens barrel must be separately manipulated, such that frequent erroneous adjustments result in a dark room.